The Treaty of Versailles had forbidden Germany from having any submarines. To get round this, German submarine crews trained in Spain and Russia. Crews also trained in anti-submarine warfare (which Versailles did not forbid) in Germany and the very nature of this meant that they had to gain knowledge of submarines themselves. Either way, by 1939, Germany had nearly 50 operational U-boats for the war. Ten more had been built but were not fully operational in September 1939.

Germany had a well respected short history of submarine building. The success of the German submarines during World War One had been startling and at the end of the war, those U-boats that had survived were surrendered to the Allies. Britain, America, Japan etc all took their share of the U-boats and used them as templates for their own versions. In 1923, Britain launched her X1 submarine which was based on the uncompleted U173 class of German submarine.

From 1918 on, Germany was technically not allowed to have submarines or submarine crews. However, no mechanisms were in place to stop research into submarines in Germany and it became clear that during the 1930’s, Germany had been investing time and men into submarines. During the same time, Britain had built 50 submarines, America 28 submarines and France 83. Even Russia, during the wars, had built over 100 submarines despite the political dislocation that country had suffered. Many of these submarines were designed by Germans – both Germany and Stalin benefited from this as Russia got the submarines she so desperately needed and Germany got the design experience.

When Hitler announced that Germany would openly re-arm, the German Navy already had considerable experience in submarine design. Under Hitler, there was no reason to hide such knowledge and five types of submarines were considered;

1) Sea-going submarines of 500 to 700 tons

2) Ocean-going submarines of 1,000 tons

3) U-cruisers of 1,500 tons

4) Coastal submarines of 250 tons to 500 tons

5) Mine laying submarines of 250 to 500 tons

Designs that included U-boats that carried two E-boats or planes were dropped.

The first sea-going U-boat was U-27 launched in 1936. By 1939, a newer model had much better engine power and greater fuel carrying capacity – the Type VII B. By 1941, this had been overtaken by the Type VII C. These were so successful that over 600 were built. The Type VII was developed from the Finnish Vetehinen design.

The Type VII C was 220 feet long and displaced about 770 tons on the surface. This U-boat had saddle tanks, four bow tubes and two stern tubes. Her diesel engines gave a top speed of 17 knots on the surface and 7.5 knots underwater. Its only drawback – a major one – was its limited range of operation; 6,500 miles at an average speed of 12 knots. However, her simple design meant that repairs at sea were relatively easy and the Type VII C had a very good reputation for reliability. The Type VII became the standard design for Germany’s submarine fleet during World War Two.

U-boats had a number of spectacular victories at the start of the war. The sinking of the liner ‘Athenia’ by U-30, though it went against Hitler’s express orders, showed how vulnerable unescorted ships were against a submarine. The British aircraft carrier ‘Ark Royal’ narrowly missed being hit by U-39 in September 1939 and in the same month the aircraft carrier ‘Courageous’ was sunk by U-29. In October 1939, U-47 carried out the most spectacular raid by penetrating Scapa Flow and sinking the battleship ‘Royal Oak’ with the loss of 833 lives. In reality, ‘Royal Oak’ was an old second line battleship. But the psychological impact of what U-47 had done was massive. One U-boat forced the Home Fleet to move from Scapa Flow to a series of temporary anchorages primarily around the coast of Scotland – but away from what was considered to be a secure harbour. The importance of this went further as U-47 had done a great deal to undermine the plans of the Admiralty which were to pin the German surface fleet in the North Sea and block any moves into the Atlantic.

The Germans did not rest on the laurels of the Type VII. The Type IXB was an ocean-going submarine and, therefore, had to have a greater range than the Type VII. This meant that it was on little value around the coast of Britain as Type VII’s could do this task. The Type IXB was used in mid-Atlantic and other zones away from their bases. They had one major drawback – they took too long to build. But with a surface weight of 1,051 tons and a surface speed of 18 knots and an underwater speed of 7 knots, Type IXB’s (carrying 22 torpedoes) were formidable weapons at sea.

If the design of the U-boats was good, their weapons were less reliable. In the first few months of the war, German torpedoes proved less than reliable. In 30 attacks by U-boats in the spring of 1940, in which captains claimed a direct hit by their torpedoes, only one ship was sunk by U-4. Therefore, the Kriegsmarine put a great deal of effort into developing a torpedo that was effective and reliable. A U-boat all but gave its position away to a ship when it attacked it but a torpedo did not explode – the wake from the torpedo was a clear indicator of the direction that the U-boat had to be in.

The collapse of France in June 1940 did a great deal to change submarine warfare. U-boats now had open access to the Atlantic from bases on the western coast of France. Prior to this, U-boats had to move either through the North Sea of the English Channel to get to the Atlantic. Both journeys were fraught with dangers. After June 1940, this problem disappeared. Twelve U-boat flotillas were based in Brest, La Rochelle, La Pallice, St Nazaire, Lorient and Bordeaux. Being so much nearer to the Atlantic also gave the Type VII more time at sea as its range at sea no longer had to include the journey from bases in Germany itself – saving many miles of travel.

Now with open access to the Atlantic, the U-boats presented a far greater threat than before. In August 1940, Hitler effectively lifted any restrictions to U-boat activity. However, the success of the ocean-going U-boats was not matched by a similar success around the coast of Britain. British coastal defences had become a lot better as the war had gone on and far more dangerous for the smaller coastal submarines used by the Kriegsmarine. But out in the Atlantic, U-boats took their toll. Between June and November 1940, 1.6 million tons of shipping was sunk – a loss rate that Britain could not sustain.

However, the German war machine could not produce enough U-boats fast enough. The Kriegsmarine had developed its requirement strategy around the war being over quickly. 60 U-boats were launched in 1940 – but this represented just over one per week. In the same year, 32 had been lost in action and 2 damaged in accidents. Submarines belonging to France and their bases had been deliberately damaged in the days leading to the surrender of France – so few of these French submarines were serviceable. At any one time during the so-called ‘Happy Times’ for U-boats, there were only ever a maximum of 30 at sea. For an area the size of the northern Atlantic, this was not many. Despite this, they managed to wreak havoc. Individual U-boat captains like Kretschmer were responsible for the sinking of 200,000 tons of shipping alone. If more U-boats had been at sea, the impact of the Battle of the Atlantic could have been far greater for Britain.

Grouped into wolf-packs, these U-boats sank vast numbers of merchant ships in the Atlantic. This peaked in 1942. U-boat captains quickly realised that a night attack made them all but invisible to an escort to the merchant ships. ASDIC was designed for underwater detection – U-boats on the surface were safe from this. At night the silhouette of a surfaced U-boat was barely visible. Kretschmer actually took his U-boat into a convoy at night as he believed that no escort commander would ever believe that a U-boat would ever deliberately go into a convoy to attack. Wolf-pack attacks were aided in their success by Focke-Wolf Condor reconnaissance planes which found where a convoy was and relayed all the relevant information back to U-boat headquarters.

For all the success of the U-boats, the Allies were developing a large array of anti-submarine weapons including more modern depth charges, ‘hedgehogs’, ‘squids’ and more sophisticated radar equipment, including radar designed to see U-boats on the surface at night. While the U-boats were successful, they were also becoming more and more vulnerable to an attack.

America’s entry into the war in late 1941, gave the U-boats new targets along the east coast of America and in the Caribbean. In the first six months of 1942, 21 U-boats sunk 500 ships. America’s navy used what it decided would be an aggressive force against the U-boats – and this excluded convoys to start with which they saw as being too passive. Destroyer patrols attempted to find U-boats and sink them. However, the U-boat captains were too skilled for this and by June 1942, America started to organise its merchant ships into convoys – such were the losses. But America’s entry into the war had major consequences for the U-boat campaign.

Britain, as an ally to America, could now move some of her shipbuilding work to the safety of America’s docks on the eastern seaboard. Britain’s ‘River’ class escort frigate was built in America and 25 ‘Flower’ class corvettes were transferred to the United States Navy. While merchant shipping losses had been very high (1,299 ships in 1941 and 1,662 in 1942), America had started to produce her legendary ‘Liberty’ and ‘Victory’ ships in vast numbers. These ships could be escorted by the new ‘River’ class frigates which could cross the whole Atlantic and remain with a convoy as a result. Faster than a surfaced U-boat, the ‘River’ frigate posed a real problem to the U-boats. Equipped with H/F-D/F radar (Huff/Duff), they could ‘see’ U-boats on the surface at night and attack.

U-boats also faced serious threats from the air. The VLR (Very Long Range) Liberator bomber and the Short Sunderland were potent weapons. The development of the MAC-ship (Merchant Aircraft Carrier) allowed for 4 planes to be carried and launched at sea.

However, U-boat development did not lag behind. Scientists in Germany had developed new torpedoes – the T4, which was replaced by the T5. The T5 (known by the British as the ‘gnat’) was a homing torpedo which traveled relatively slowly but was very accurate. The newly developed radar impulse director (RID) also gave the U-boats a greater degree of forewarning that enemy ships and planes were around.

During 1943, the ‘Happy Days’ were coming to an end for the U-boats. Scientific developments and new tactics spelt the end for the U-boats. The British organised ‘convoy support groups’ for the convoys. These were ships that went to look for U-boats away from a convoy but could return to that convoy quickly if required. While these ships were away, the convoy was still guarded by escorts. However, 1943 started off well for the U-boats. Cryptanalysts in Germany had cracked the British convoy cypher and a large wolf-pack of 39 U-boats was sent by Dönitz to attack convoys 5C-122 and HX-229 – two eastward bound convoys in March. A total of 21 merchant ships were lost (140,000 tons) with only three U-boats lost. This was the high watermark for the U-boats in 1943.

Many vital vessels had been used in ‘Operation Torch’ – the invasion of Sicily in 1943. With these vessels no longer being needed, they could be used on escort duty in the Atlantic. This greatly helped the convoys. Secondly, 61 VLR Liberators were made available to the RAF as a result of the intervention of Roosevelt. This gave the convoys a much greater aerial cover. But the biggest contribution was scientific. Aircraft were fitted with ASV (Air to Surface Vessel radar). This allowed a plane to spot a U-boat on the surface but the U-boat could not pick up ASV on its radar receiver. Therefore a plane could attack a surfaced U-boat in the knowledge that it did not know it was about to be attacked. In May 1943, a wolf-pack of 12 U-boats attacked another convoy but 8 U-boats were lost. For the first time in months, the Germans were faced with a major dilemma.

A U-boat attacked from the air

Dönitz now made two mistakes. He ordered that all U-boats should be fitted with more anti-aircraft guns. He believed that planes would think twice when faced with greater fire from a U-boat. However, he miscalculated. If a plane was fired at (and Liberators and Short Sunderlands were not the fastest of planes) they simply stayed out of range and relayed the position of the U-boat to the nearest escort ship. If the U-boat then tried to dive, putting its guns out of use) the plane would attack. U-boat crews gave themselves a window of between 30 and 40 seconds to submerge before a plane got within range to attack.

The second mistake concerned radar. U-boats were fitted with a Metox receiver that detected if a submarine was being searched for by radar. U-boat commanders reported that they were being attacked on the surface at night by planes but that Metox had given no sign that any plane was in the vicinity using radar on the U-boat. It was found that Metox gave off an emission that could be tracked and the Germans concluded that Metox was to blame for all their recent losses in 1943. It was replaced and the Germans were satisfied that the problem had been solved. They did not realise that it was because the ASV was so accurate in pin-pointing U-boats, hence no attempt was made to hinder the work of the ASV radar.

By mid-1943, convoys were having far greater success in getting to Britain. In May, two convoys reached Britain without losing a single ship – and 6 U-boats had been lost. Between April 1943 and July 1943, 109 U-boat were lost. Dönitz withdrew his U-boats from the battle as a temporary measure. German scientists worked on methods to boost the defences of the German submarines. New engines were developed such as the Walther propulsion system; hulls were coated with rubber in the belief that they would absorb ASDIC (they did not!) and new submarines were designed. The most famous was the Type XXI. This had a streamlined hull, an enlarged battery for greater endurance and greater speed. The Type XXI was an awesome weapon but too few were ever produced. The Allies could now bomb factories and submarine pens with great frequency and accuracy. Fuel depots were also a target. The Germans may have had a fine submarine on paper but producing it in numbers was a different matter. Dönitz informed Hitler that the first Type XXI would be ready by November 1944. Hitler ordered an earlier date and gave Albert Speer the task of getting the Type XXI produced. But with the Allies and the Russians closing in on both sides of Europe, constant bombing of factories etc, it was an impossible demand. Also the demands of the army and Luftwaffe also hit the U-boats. Steel was vital to U-boat production – but it was also vital to the other parts of the military as well. The army also demanded men and the movement of men into the army meant that the navy did not get the men it needed. The U-boat service suffered accordingly.

The Type XXI was commissioned in early 1945 and the first one, U-2511, went to sea just one week before Germany surrendered. On May 7th, 1945, Dönitz ordered all U-boats to cease hostilities.